perf ftrace: Remove needless code setting default tracer

As a result of commit a3497642c261 ("perf ftrace: Make 'function_graph'
be the default tracer") the ftrace.tracer variable can't be NULL but the
other code setting default tracer remained.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1485423339-22780-1-git-send-email-treeze.taeung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-ftrace.c

@@ -202,7 +202,7 @@ int cmd_ftrace(int argc, const char **argv, const char *prefix __maybe_unused)
 {
 	int ret;
 	struct perf_ftrace ftrace = {
-		.tracer = "function_graph",
+		.tracer = DEFAULT_TRACER,
 		.target = { .uid = UINT_MAX, },
 	};
 	const char * const ftrace_usage[] = {
@@ -231,9 +231,6 @@ int cmd_ftrace(int argc, const char **argv, const char *prefix __maybe_unused)
 	if (ret < 0)
 		goto out_delete_evlist;
 
-	if (ftrace.tracer == NULL)
-		ftrace.tracer = DEFAULT_TRACER;
-
 	ret = __cmd_ftrace(&ftrace, argc, argv);
 
 out_delete_evlist: